Laser processing of material, specifically the controlled interaction of laser light with material, is well established in various fields of applications such as laser cutting and laser welding, be it, for example, in industrial as well as medical applications. The interaction depends on the laser light parameters such as wave length, focus zone, laser power etc. as well as the material properties such as absorption at the respective wave length, band gap of the material etc. In combination, those parameters and properties define the interaction that takes place and in particular the field strength that is provided at a specific position within the material. A thermal approach is disclosed in US 2009/0294419 A1 using a system for laser scoring of non-flat materials based on thermal shock generation by a moving laser beam and with subsequent local cooling.
US 2011/0183116 A1 and US 2012/0064306 A1 disclose examples for laser processing methods for cutting glass, specifically tempered glass. In particular, for tempered glass the internal stress distribution affects the cutting. Accordingly, US 2012/0064306 A1 discloses not to treat the cutting region while US 2011/0183116 A1 disclose providing a trench structure formed in a compression stress layer along a predetermined cutting path.
A method for fabricating strengthened glass panels from glass substrate sheets is disclosed in 2012&0196071 A1. Therein, at first holes are prepared, e.g. by laser processing, mechanical drilling or etching processes, and then the strengthening process is applied, i.e. after the formation of the series of holes. This results in radially compressive stress layers formed along the wall sides of the holes.
Specifically when applying pulsed laser systems, laser pulse energies as well as laser pulse durations may be well controllable and, thus, be adapted to the specific application. JP 2005/288503 A discloses a laser beam machining method based on a laser light interaction that uses self-focusing as well as a Bessel beam shape for cutting glass prior treatment.
The use of Bessel beams for laser processing is disclosed, for example, in “High aspect ratio nanochannel machining using single shot femtosecond Bessel beams” by M. K. Bhuyan eta al., Applied Physics Letters 97, 081102-1 (2010) and “Femtosecond non-diffracting Bessel beams and controlled nanoscale ablation” by M. K. Bhuyan et al., IEEE (2011).
WO 2012/006736 A1 discloses a method for laser cutting of transparent materials by irradiating the substrate with, for example, a burst train of pulses of a focused laser beam, wherein the focusing condition, the pulse energy and duration were selected to produce a filament within the substrate and the substrate is translated relative to the laser beam. According to WO 2012/006736 A1, filaments are produced by weak focusing, high intensity, short duration laser light, which can self-focus by the nonlinear Kerr effect, resulting in an increase of the peak intensity and the creation of a low-density plasma in the high-intensity portion of the laser beam. In WO 2012/006736 A1 it is further stated that the method avoids dense plasma generation such as trough optical breakdown that may be easily produced in tight optical focusing conditions, wherein the plasma generation mechanism is based on initial multi-photon excitation of electrons, followed by inverse Bremsstrahlung, impact ionization, and electron avalanche processes. According to WO 2012/006736 A1, in this optical breakdown domain the singulation, dicing, scribing, cleaving, cutting and facet treatment of transparent materials has disadvantages such as slow process speed, generation of cracks, contamination by ablation debris, and large kerf width.
The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems and in particular to providing high precision cutting of tempered glass, which still remains a challenge of the present day technology.